1. Field of the Invention
The present invention relates to a response characteristic estimation technology and a receiving technology utilizing the same. It particularly relates to a weighting coefficient estimation method and apparatus, and to receiving method and apparatus, where those methods and apparatuses are utilized for synthesizing radio signals received by a plurality of antennas.
2. Description of the Related Art
In wireless communication, it is in general desired to effectively use limited frequency resources. In order to use the frequency resources effectively, radio waves of same frequency are, for example, utilized as repeatedly as possible in short-range. In this case, however, communication quality degrades because of cochannel interference caused by a radio base station or mobile terminal closely located, which utilizes the same frequency. As one technology for preventing such communication quality degradation deriving from the cochannel interference, the adaptive array antenna technology can be named.
In the adaptive array antenna technology, signals received by a plurality of antennas are respectively weighted with different weighting coefficients and synthesized. The weighting coefficients are adaptively updated so that an error signal between a signal to be transmitted and the signal after the synthesis might be small. Here, the signal to be transmitted is determined based on the signal after synthesis. In order to update the weighting coefficients adaptively, the RLS (Recursive Least Squares) algorithm, the LMS (Least Mean Squares) algorithm or the like is utilized. The RLS algorithm generally converges at high speed. The RLS algorithm, however, requires a high speed or a huge arithmetic circuit since computation performed is very complicated. The LMS algorithm can be realized with a simpler arithmetic circuit than that of the RLS algorithm. However, the convergence speed thereof is low.
Related Art List
1. Japanese Patent Application Laid-Open No. 2002-26788
A technology of determining weighting coefficients by correlation processing between a known transmission signal and a received signal is one that can determine the weighting coefficients at high speed with a simple circuit. However, unlike the adaptive algorithm, the technology utilizing the correlation processing can not track an environmental change. For example, if there is frequency offset between the frequency oscillators of a transmitter and a receiver, the frequency offset is reflected to the weighting coefficients as an error. If the weighting coefficient including an error is utilized in the adaptive array antenna technology, receiving characteristic generally degrades.